Touch screens are more and more commonly used for various computer applications and for office machines such as copy machines, fax machines, graphical scanners etc. Typically a touch screen takes the place of a normal computer screen, a keyboard and/or optional peripheral equipment such as a pointing device in the form of a mouse or a track ball. In addition to the ability of displaying an image, a touch screen has a matrix with a plurality of sensitive points defined on the surface of the screen. By touching a point on the screen, the absolute position of the point on the screen being touched is registered and transmitted to the controlling CPU. This is similar to pressing a mouse button where the absolute position of a cursor is registered.
When defining a relative position or a movement of an item e.g. when dragging and dropping items on the screen, the mouse button is typically kept depressed while the cursor is moved from one position on the screen to a new position on the screen. The desired result, be that a vector defining the change in the size of the item or a vector defining the distance and direction of the movement of the item, is defined from the start point, at the time when the mouse button is depressed, to the end point, when the mouse button is released. Since applications using touch screens typically has no conventional pointing devices, such as a mouse or trackball, a similar user interface may be difficult to achieve. Applications exist wherein the start point is defined as the point a user touches the screen and by keeping the finger in contact with the screen, the user may move the finger to the end point where the finger is removed from the screen. However, it is typically an awkward process to move a finger in firm contact with a screen and due to the sensitivity of common touch screens, the above mentioned user interface for defining a relative position or movement on a screen is not suitable for many applications. As an example, the user may often have to press relatively hard against the surface of the screen in order to activate the sensitive areas of the screen and it is difficult at one time both to press hard against the screen and move the finger across the screen.